Phase stability ofTi2AlCupon oxygen incorporation: A first-principles investigation

Abstract

The phase stability of Ti 2 AlC upon oxygen incorporation has been studied by means of first-principles calculations. Recent experimental observations of this so-called MAX phase ͑M = early transition metal, A = A-group element, and X = C or N͒ show that the characteristic nanolaminated structure is retained upon oxygen incorporation, with strong indications of O substituting for C. Therefore, a solid solution of C and O on the carbon sublattice has been simulated by the so-called special quasirandom structure method. Through a developed systematic approach, the enthalpy of formation of Ti 2 Al͑C 1−x ,O x ͒ has been compared to all experimentally known competing phases, and has been found favorable for all C to O ratios at the composition of the MAX phase. A negative isostructural formation enthalpy has also been predicted for Ti 2 Al͑C 1−x ,O x ͒. Altogether, the results indicate that a large amount of oxygen, at least up to x = 0.75, might be present in the Ti 2 AlC MAX-phase structure without decomposition of the material into its competing phases. Furthermore, an effect of an increased oxygen content is a corresponding increase in the bulk modulus and a change in electronic properties. These results are of importance for further understanding and identification of possible composition range of the MAX-phase oxycarbide, and hence for the prospect of tuning the material properties by a varying incorporation of oxygen.

Magnetic MAX phases from theory and experiments; a review

“…Phase stability calculations at 0 K have been proven successful when it comes to verify existing [12,14,22,26,81,[84][85][86] and, more importantly, predicting new MAX phases and related materials [3,7,25,87]. When it comes to magnetic MAX phases, almost all calculations to date neglect effects from temperature.…”

Synthesis of Ti3AuC2, Ti3Au2C2 and Ti3IrC2 by noble metal substitution reaction in Ti3SiC2 for high-temperature-stable Ohmic contacts to SiC

“…Further details are given in Refs. 10,11 To determine the dynamical stability of the studied ordered structure, we performed phonon calculations using the small displacement method, supercell sizes of at least 3x3x1 unit cells, along with the code Phonopy 12 . Density of states (DOS) and chemical bonding were investigated in terms of projected crystal orbital Hamiltonian populations (pCOHP) which were derived using the LOBSTER program 9,12,13 .…”

Synthesis andab initiocalculations of nanolaminated (Cr,Mn)2AlC compounds

“…X-ray diffraction in combination with analytical transmission electron microscopy, including electron energy-loss spectroscopy and energy dispersive x-ray spectroscopy analysis, revealed that the films were epitaxial (0001)-oriented single-crystals with x up to 0. 16 MAX phases constitute a family of inherently nanolaminated compounds with a general composition of M n+1 AX n , where M denotes an early transition metal, A is an A-group element, and X is C and/or N. 1 Presence of both metallic and covalent bonds between different layers provides a unique combination of metallic and ceramic properties, such as high (anisotropic) conductivity, hardness, and thermal shock resistance. 2 Fascinating MAX phase phenomena range from extreme damage tolerance including reversible deformation 3 over oxidation induced self-healing behavior 4 to stability of nanosheets upon exfoliation.…”